Serow 225

Hello All

This was to have been my entry in the 6.KBW, but I looked again at the rules, and found that it will not be eligible as scaling is not allowed. This will therefore have to be an ordinary contruction report.

The prototype is an off-road trail bike which has been manufactured in slightly varying versions since 1985, and is still available, at least in Japan.

The model is a free download from Eastern's Toybox (http://www.saturn.dti.ne.jp/~eastern) which appeared in January to join his large selection of rally cars and aircraft. It has 9 A4 pages containing a little under 300 parts, and is at scale 1:8. There are four pages of diagrammatic instructions with some Japanese text on them. Unfortunately the instruction PDF file is locked to prevent text extraction, so it is not possible to present the text to an online translator.

A first inspection of the parts file showed good clear computer graphics, but with rather heavy black outlines suggesting possible problems with light-coloured parts. Conversely, fold lines show very little contrast against the part colouring, particularly on the dark green of the frame, fuel tank and seat.

I wish this to match my collection of motorcycle models from Yamaha in scale. As nearly as I can tell those are scale 1:7, and I have made them half-size, so I constructed high-resolution bitmaps at a relative scale of 8:14, or 57%. I do not have a capable vector picture-processing program, or expertise in using one, so I do any manipulation necessary on the bitmap. In this case, I toned down the black outlines around light-coloured parts to a mid grey before printing the pages. I haven't printed the two pages containing the wheel hubs and spokes, as I think I shall have to use a different technique to build the wheels in this scale.

More soon,
Alan

I decided to start with the frame, though it is stage 2 on the instruction sheets, stage 1 being the fuel tank, seat, instrument panel and mudguards (fenders). My experience is that assembling a tubular frame is hard, so I wanted to get it out of the way before committing myself to a lot more construction.

The ends of the tubes are festooned with tiny tabs to fit inside the next one along. There is no way I can get this to work, so I cut off all the end tabs, and drew joining pieces crooked at different angles. The angles I obtained by measuring the amplitude of the sine waves on the joining ends. The design of the joining piece I have shamelessly stolen from Greelt Peterusma's F1 rocket engine model, though his are only right-angled. I forgot to photograph them, so the pictures are from my Yamaha YZF-R1 build.

To help get the shape right, I built in the central block right away, though the instructions advocate sliding it in as part of final assembly. As it turned out, it wasn't too hard to build a reasonable-looking frame, though the top tubes didn't fit well against the squared-off link between the front and rear sections. Fortunately this will eventually be covered by the seat. Time will tell whether the frame is accurate enough for everything else to fit.

Alan

The next thing to be fitted to the frame is the rear arm. This is the usual U-shaped assembly, which I usually find difficult to make without twist in the arms. This one seemed to go better than usual, though I don't really know why.

Attachment to the frame is by an oddly-shaped bracket underneath and the spring assembly above, which passes right through the middle of the frame to attach to the top tube. This required some fiddling to get in place, but rather to my surprise fitted perfectly once in place. The frame has passed its first test.

Alan

Gert

Thank you. On the whole the model is fairly simple (especially compared with the Yamaha MT-01!), but quite satisfying. I can see that there are some tricky bits to come, though...

Alan

The engine assemply is very simplified - three main blocks with a few add-on details - but will probably be adequate in context. The junction between the lower part of the cylinder and the crankcase shows evidence of an automated "unfolding" process (Pepakura?). Instead of simply gluing the cylinder to the top of the crankcase, the latter is cut away leaving tabs to be folded upwards to fit inside the cylinder block. I chose to ignore this, and added tabs to the cylinder to attach to the unbroken top of the crankcase.

The rear of the engine is attached to the bottom of the frame, and you will see a white strip about half-way up the rear section indicating the attachment point. This is wrong - in order for the engine to fit properly it is the bottom edge which needs to be attached. Luckily I was able to prise the original glue join apart without destroying either the engine or the frame.

The front part of the frame slides into the top tube and attaches to the lumps at the front of the engine, but I shall not fix it until I have added the front forks and handlebars to it.

Alan

Hi Modelschiff

I don't seem to be able to get the engine to start. Maybe that is really true to the prototype!

Alan

Hello All

Not a lot of progress in the last three days - I seem to have had too many other things to do. The engine undertray is not very prettily done, but hardly any of it will show when it is fitted, so I am hoping that it will be adequate. I am not sure I could do any better on a second attempt, anyway.

Alan

A few more pieces, but I can't put off doing the hard bits any longer. Tomorrow I must start on the front forks!

Alan

Here is the reason I put off the front forks. Forty-four tiny rings to be made up and threaded on the rods to simulate the bellows covering the suspension mechanism. In fact it wasn't as difficult to do as I expected, especially as I saw in photographs of the real thing that these bellows get a bit uneven after use. I console myself with the thought that the irregularity in mine is highly realistic. As you can see I printed off a good number of spares, but as it turned out I only needed to use four of them.

I am now going away for a few days, so there will be no progress for a little while.

Alan

Hello again

Back to work again. The front forks turned out not to be so fearsome after all. Fitting the straps (C38) which hold the meter/headlamp assembly to the upper fork tubes was quite awkward - I got one side a bit skew, but I hope it doesn't notice too much. The bar in front of the headlamp was also quite a struggle, as it is so thin, being only 1mm internal diameter.

The handlebars are slightly larger tubes, but still quite difficult to set up accurately.

One small problem is that several parts are duplicated in left/right mirrored form, and some are labelled L/R incorrectly. This is the case for the above-mentioned straps C38 and the side pieces of the headlamp bar C26 and C27. (It was also true for the frame brace C2, but I forgot to mention it at the time.)

Alan

The front frame and forks are now in place.

Have you spotted the "deliberate mistake"? Just before doing this assembly, I was studying the drawings showing the way the control cables run from the handlebars to the front brake and engine. On my model there was no mark on the carburettor for the end of the throttle cable. I had put the carburettor on upside down. Fortunately there was just enough room to cut it away and refit it the right way up.

Alan

The exhaust pipe was a bit of light relief. The tubes are over 2mm internal diameter, so felt enormous compared with what I have been doing. As usual I cut off all the tabs from the tubes and used elbow pieces to join them at the correct angles. For the larger joins between the conical sections and the silencer cylinder I used an internal joining strip to ensure a smooth join.

The fuel tank wasn't too easy because of the grilles at the front. The internal pieces are halved together, and also into the internal layer of the double-thickness surround. I felt that this latter would make the surround piece far too fragile, and that it was quite unnecessary, so I cut off the projecting portions and just butt-jointed them to the surround. The result is not gloriously beautiful, but reasonable enough at this scale. [The picture comes out rather over three times the actual size of the part on a normal monitor screen.]

Alan

And so to the wheels ...

The kit provides four sets of spokes for each wheel, made from double-thickness card. Each set has nine spokes which are just about 1mm wide. In my reduced scale, this will come out at just over 0.5mm. This represents 8mm in full scale, which is still subtantially overscale. In any case, I don't feel confident about cutting and handling such delicate things, so I am going to make my wheels using silver thread for the spokes, as I have done a couple of times before.

The first thing to do is to draw the flanges to take the inner ends of the spokes. Each has three layers, which are strengthened with cyano. The outer ones each have a ring of eighteen spots, half of which are drilled for the spokes, the remainder representing the riveted ends of the spokes on the other side. When assembled, these holes are arranged alternately, and the inner layer has nine slots to link adjacent holes on the two sides, and allow the thread to run between them. Each thread thus forms two spokes. Two flanges attached to a separator form the hub.

The other thing I draw is a circular frame with the spoke runs drawn on it. This is built up to approximately the same thickness as the hub, so that when the spokes run from one flange to the opposite side of the frame, they pass through the centre plane roughly midway. This is where the wheel rim goes. The rim has 36 holes along its centre line for the spokes to pass through, so the next task is to thread the spokes through the right holes, making sure that they cross the correct side of each other and don't get twisted. This makes the mess shown in the third picture.

Then the spokes are drawn up taut (but not tight), holding their ends in slots on the edge of the frame, until the hub is suspended in the centre. Finally I run a fillet of epoxy all round the centre of the rim to lock the spokes in place (last picture).

Alan

Finally the rest of the wheel and tyre is made up from kit parts, and fitted into the rear arm.

Alan

Thorsten

Thank you for your comments. I get an almost magical thrill when these limp and weak materials suddenly become strong and stiff by applying well-balanced forces. Isn't engineering wonderful?

I agree with you that the very simplified engine rather lets down the rest of the model. Without really thinking about it I rather assumed that it would be better hidden by the fuel tank; otherwise I might have tried to modify it with a bit more detail.

Alan

The hub of the front wheel is a bit unusual. Instead of a simple flange with the spokes emerging alternately from each side, the flanges are dished. All the spokes pass through in the same direction, but through two staggered rings of nine holes each. This is shown clearly on this photograph from wemoto.com:

1992 Serow 225

This is a photograph of a 1992 model, with a silver coloured hub. The model appears to be of a 1985 model, which seems to have had a dark-coloured hub (see 1985 Serow 225 from topsk.com), so this is what I chose.

I simulated the arrangement with conical flanges, guessing reasonable-looking dimensions from the photographs. Please excuse the rather rough appearance in the photograph of the hub - my excuse is that the photograph comes out at about 8 times actual size on most monitors. The rest of the construction is just the same as for the rear wheel, except that because it is a much narrower tyre it is much harder to avoid distortion.

Alan

Just a few small items - footrests, pedals, mirrors, kick stand - and it is done, finished, fertig! Model number 16 in my motorcycle collection.

Fairly convincing.

Alan

Dear Wolfgang

Thank you for your kind comments. I too like the "proper" wire wheels, though they are quite stressful to make. At several points, even a small mistake means that everything done already must be scrapped. Luckily that didn't happen this time for either wheel.

You might regret asking about the other 15 bikes! It just so happens that they all appear on my web site where you can be bored to death for hours.

Best wishes,
Alan